Board.toList: use foldl because insertion order matters
changed Go.Board.FFI.insert to Go.Board.FFI.insert' because it handles (Maybe Stone), which is considered an aux featured compared to Stone; added to Go.Board { null, size, singleton, singleton', insert, insert', insertWith, insertWith', delete, adjust, adjust', toList, toList', fromList, fromList', elems, elems' }